High energy, real time capable, direct radiation conversion X-ray imaging system for Cd-Te and Cd-Zn-Te based cameras

Abstract

A calibrated real-time, high energy X-ray imaging system is disclosed which incorporates a direct radiation conversion, X-ray imaging camera and a high speed image processing module. The high energy imaging camera utilizes a Cd—Te or a Cd—Zn—Te direct conversion detector substrate. The image processor includes a software driven calibration module that uses an algorithm to analyze time dependent raw digital pixel data to provide a time related series of correction factors for each pixel in an image frame. Additionally, the image processor includes a high speed image frame processing module capable of generating image frames at frame readout rates of greater than ten frames per second to over 100 frames per second. The image processor can provide normalized image frames in real-time or can accumulate static frame data for substantially very long periods of time without the typical concomitant degradation of the signal-to-noise ratio.

What is claimed is: 
     
       1. An x-ray imaging device ( 28 ), comprising:
 a camera radiation detector substrate comprised of an array of pixels, 
 each pixel collecting electrical charges generated responsive to absorption of radiation energy, 
 the collected electrical charges defining an uncorrected image pixel value of the corresponding pixel; 
 an output for producing multiple different image frames ( 44 ), each frame comprising an array ( 45 ) of the uncorrected image pixel values from the detector substrate; 
 a correction part ( 20 ,  49 ,  22 ,  24 ) for individually applying an individualized, pixel-specific calibration correction function to each of the uncorrected image pixel values of the output, including offset correction, for correcting the uncorrected image pixel values from each frame of the different image frames to provide a normalized image data to a display for presenting an x-ray image, 
 the calibration correction function being specific to each of the uncorrected image pixel values of the output of each frame; and 
 a processor ( 24 ) for calculating the individualized specific correction function for each of the uncorrected image pixel values of each frame, the specific calibration correction for each image pixel value ( 47 ) of said normalized image data being derived from a plurality of corrected individual single frame image pixel values ( 36 ) of said multiple different frames corrected by said specific correction functions. 
 
     
     
       2. The device ( 28 ) of  claim 1 , wherein,
 said correction part utilizes incoming intensity of the absorbed radiation energy to normalize the individual pixels with respect to one another, and 
 the calibration correction function for each uncorrected image pixel value is independent of the calibration correction functions for at least some of the other image pixel values of the output of each frame. 
 
     
     
       3. The device ( 28 ) of  claim 1 , wherein,
 the calibration correction function utilizes different pixel-specific polynomial functions for each of different pixels, each respective calibration correction function providing a pixel specific correction coefficient independent of the calibration correction coefficient for other image pixel values of the output of each frame. 
 
     
     
       4. The device ( 28 ) of  claim 1 , wherein,
 the uncorrected image pixel value of each pixel indicates an intensity of the radiation energy absorbed on the associated pixel, 
 the calibration correction function utilizes different pixel-specific polynomial functions for each of different pixels, each respective calibration correction function providing a pixel specific correction coefficient independent of the calibration correction coefficients for other image pixel values of the output of each frame, 
 each of the different pixel-specific polynomial functions provides a mapping from the uncorrected image pixel value (x in ) to a global output value so each pixel gives the same output as all the other pixels for the same intensity of the absorbed radiation energy, 
 the polynomial function of each pixel being: 
 
       
         
           
             
               
                 y 
                 out 
               
               = 
               
                 
                   ∑ 
                   
                     i 
                     = 
                     0 
                   
                   M 
                 
                 ⁢ 
                 
                   
                     a 
                     
                       i 
                       , 
                       pix 
                     
                   
                   ⁢ 
                   
                     x 
                     in 
                     i 
                   
                 
               
             
           
         
         wherein a i,pix  are the coefficients for each pixel pix, M is the order of the polynomial, and x i   in  are the uncorrected image pixel values for each pixel. 
       
     
     
       5. The device ( 28 ) of  claim 1 , wherein,
 the camera radiation detector substrate is a high pixel density, direct conversion radiation detector substrate ( 30 ), and 
 further comprising: 
 a high energy x-ray imaging camera ( 37 ), 
 the camera including a camera module ( 12 ) having the high pixel density, direct conversion radiation detector substrate ( 30 ), with the pixels ( 36 ) of the detector substrate in electrical connection to a corresponding pixel circuit ( 31 ) on an ASIC readout substrate ( 32 ), 
 the detector substrate providing for directly converting impinging high energy x-ray and gamma ray radiation ( 80 ) to an electrical charge and communicating the collected electrical charge via an electrical connection ( 35 ) between the pixel ( 36 ) to a corresponding pixel circuit on the ASIC readout substrate ( 32 ) as an electric charge signal of the uncorrected image pixel value, and the pixel circuit providing for processing the electric charge signal of the uncorrected image pixel value from each pixel. 
 
     
     
       6. The device ( 28 ) of  claim 5 , wherein the camera includes a detector substrate bias switch circuit ( 121 ). 
     
     
       7. The device ( 28 ) of  claim 5 , wherein the camera comprises a Cadmium Telluride composition based radiation detector substrate ( 30 ) in communication with the ASIC readout substrate ( 32 ). 
     
     
       8. The device ( 28 ) of  claim 7 , wherein the camera comprises the radiation detector substrate ( 30 ) being a composition selected from the group consisting of: Cadmium-Telluride and Cadmium-Zinc-Telluride. 
     
     
       9. The device ( 28 ) of  claim 5 , further comprising a high speed image frame processing module ( 18 ) in electronic communication with the ASIC readout substrate ( 32 ) of the imaging camera ( 37 ), the frame processing module capable of receiving digitized pixel signals derived from the output from each pixel circuit ( 31 ) of the readout substrate and using the pixel signals to generate an image frame ( 44 ) at a frame readout rate of greater than ten image frames per second. 
     
     
       10. The device ( 28 ) of  claim 9 , wherein the high speed image frame processing module ( 18 ) is capable of receiving digitized pixel signals derived from the output of each pixel circuit ( 31 ) of the readout substrate ( 32 ) and using the digitized pixel signals to generate an image frame ( 44 ) at a frame readout rate of greater than 25 image frames per second. 
     
     
       11. The device ( 28 ) of  claim 9 , wherein the high speed image frame processing module ( 18 ) is capable of receiving digitized pixel signals derived from the output from each pixel circuit ( 31 ) of the readout substrate ( 32 ) and using the digitized pixel signals to generate an image frame ( 44 ) at a frame readout rate of greater than 50 image frames per second. 
     
     
       12. The device ( 28 ) of  claim 9 , further comprising a calibration module selectably in digital communication with the frame processor module ( 18 ), the calibration module when selected being driven by a software process including a calibration routine ( 20 ) which calibration routine writes pixel correction data specific to each pixel ( 36 ) in an image frame ( 44 ) to a lookup table ( 22 ). 
     
     
       13. The device ( 28 ) of  claim 12 , wherein the software process includes a calibration routine ( 20 ) which analyzes each of the digitized pixel values ( 47 ) over at least some of the collected calibration frames ( 44 ) being analyzed in accordance with a pixel value correction algorithm ( 49 ) to provide and write pixel value correction data specific to each pixel ( 36 ) in an image frame ( 44 ) to the lookup table ( 22 ). 
     
     
       14. The device ( 28 ) of  claim 12 , wherein the software driving the calibration module ( 20 ) includes a pixel non-linear performance compensation routine ( 123 ) providing error correction for each pixel ( 36 ) as a function of time. 
     
     
       15. The device ( 28 ) of  claim 14 , wherein the pixel non-linear performance compensation routine ( 123 ) includes an asymmetric linear polynomial calculation to determine correction coefficients to provide error correction for each pixel ( 36 ) as a function of time. 
     
     
       16. The device ( 28 ) of  claim 12 , wherein the lookup table is writeable by the calibration module ( 20 ) with pixel specific correction data, and readable by a normalization module ( 24 ). 
     
     
       17. The device ( 28 ) of  claim 16 , wherein the normalization module ( 24 ) is selectably in communication with the frame processor module ( 18 ) and with the lookup table ( 22 ), the normalization module receiving real time image frame data/record from the frame processor module and pixel specific correction data from the lookup table, and providing said normalized image data via a display image output for use in said display module ( 16 ) to present said X-ray image. 
     
     
       18. The device ( 28 ) of  claim 17 , wherein the normalization module ( 24 ) provides said normalized image data via said display image output for use in said display module ( 16 ) to present a dynamic X-ray image from the high energy, real time, direct detection X-ray imaging system ( 10 ). 
     
     
       19. The device ( 28 ) of  claim 18 , wherein the normalization module ( 24 ) accumulates said normalized image data over a period of time of at least one hundredth of a second to ten seconds for providing a high precision display image output for each of the accumulation periods, for use in said display module ( 16 ) to present said dynamic X-ray image. 
     
     
       20. The device ( 28 ) of  claim 17 , wherein the normalization module ( 24 ) provides said normalized image data via said display image output for use in said display module ( 16 ) to present a static X-ray image from the high energy, real time, direct detection X-ray imaging system ( 10 ). 
     
     
       21. The device ( 28 ) of  claim 20 , wherein the normalization module ( 24 ) accumulates said normalized image data over a period of time to provide a high precision display image output for use in said display module ( 16 ) to present said static X-ray image. 
     
     
       22. The device ( 28 ) of  claim 21 , wherein the normalization module ( 24 ) accumulates said normalized image data over a period of time of at least one hundredth of a second to 300 seconds. 
     
     
       23. The device ( 28 ) of  claim 9 , wherein the normalization module ( 24 ) accumulates said normalized image data over a period of time of at least five minutes.